Such an apparatus is generally known from EP 148 509 A1. The flow through the apparatus is such that in spite of the use of a pump the cleaning bodies do not pass through the latter and instead take a different flow path by means of which they can be transferred back from the heat exchanger outlet to its inlet. However, for its operation it is necessary to have two motor-operated valves and a motor-operated flap for closing and opening an opening, which links the casing having the screening device with the sink space. Thus, it is necessary to provide three separate motor drives, which in particular make smaller installations more expensive. In conjunction with the sink space below the flap serving as the casing bottom there is an infeed of cleaning bodies either directly (FIGS. 1 and 2) of the reference or via a bypass (FIG. 3) of the reference into the heat exchanger inlet. When using the bypass solution the cleaning bodies are passed out of the sink space into a partial flow branched off the main cooling water flow and are transported by it into the heat exchanger inlet. The transfer flow for the return of the cleaning bodies produced with the pump and commencing at the heat exchanger outlet is passed behind the screening device via a separate line, in which the pump is located, and consequently without the cleaning bodies into the main cooling water line or into the heat exchanger inlet. The objective of this separation is to ensure that the Cleaning bodies do not have to pass through the pump which produces the transfer flow.
U.S. Pat. No. 4,079,782 discloses an apparatus in which an outlet line, in which the pump is located, is connected to the casing. The casing has on the bottom a second outlet from which can be flushed the cleaning bodies. The pump outlet is connected to the second outlet in such a way that the water delivered by the pump and sucked out of the casing "entrains", in accordance with the Jet pump principle, a flow containing the cleaning bodies from the second outlet. Also in this known apparatus, in which the cleaning bodies circulate continuously unlike in the case of the apparatus of EP 148 509 A1, the cleaning bodies do not flow through the pump.